Thermodynamics Test

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Thermodynamics Test - 68

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Weekly Quiz Competition

Question 1
1 / -0

The favourable conditions for a spontaneous reaction are:

A
$$T\Delta S> \Delta H, \Delta H=+ve,\Delta S=+ve$$

B
$$T\Delta S> \Delta H, \Delta H=+ve,\Delta S=-ve$$

C
$$T\Delta S= \Delta H, \Delta H=+ve,\Delta S=-ve$$

D
$$T\Delta S= \Delta H, \Delta H=+ve,\Delta S=+ve$$

Solution

The free energy charge $$\triangle G$$ is given by, $$\triangle G=\triangle H-T\triangle S$$

The reaction is spontaneous if $$\triangle G<0.$$

$$\Longrightarrow \triangle H-T\triangle S<0$$

$$\Longrightarrow T\triangle S>\triangle H, \triangle H=+ve,\triangle S=+ve$$
Question 2
1 / -0

Which of the following conditions make the process non spontaneous at all temperatures.

A
$$\Delta H=+ve;\Delta S=-ve$$

B
$$\Delta H=-ve;\Delta S=+ve$$

C
$$\Delta H=+ve;\Delta S=+ve$$

D
$$\Delta H=-ve;\Delta S=-ve$$

Solution
Question 3
1 / -0

Two samples of DNA, A and B have melting points $$340K$$ and $$350K$$ respectively. This is because

A
B has more GC content than A

B
A has more GC content than B

C
B has more AT cotent than A

D
both have same AT content

Solution

The B sample of DNA having higher melting point must be having more GC content as comppared to sample A. Since GC base pair having 3 hydrogen bonds as compare to AT base pair having only 2 hydrogen bonds, results in stronger bonding.
So, option $$A$$ is correct
Question 4
1 / -0

Which of the following statements/relationships is not correct in thermodynamic changes?

A
$$w=-nRT\ln{\cfrac{{V}_{2}}{{V}_{1}}}$$ (isothermal reversible expansion of an ideal gas)

B
For a system at constant volume, heat involved is equal to change in internal energy.

C
$$w=nRT\ln{\cfrac{{V}_{2}}{{V}_{1}}}$$ (isothemal reversible expansion of an ideal gas)

D
$$\Delta U=0$$ (isothermal reversible expansion of an ideal gas)

Solution
Question 5
1 / -0

For a spontaneous reaction, the $$\Delta G$$, equilibrium constant, $$K$$ and will be respectively:

A
$$-ve,> 1$$

B
$$+ve, 1$$

C
$$-ve,< 1$$

D
$$-ve. 1$$

Solution
Question 6
1 / -0

Assuming that water vapour is an ideal gas, the internal energy change ($$\Delta U$$) when $$1mol$$ of water is vaporised at $$1$$ bar pressure and $${100}^{o}C$$ will be:
(Given: Molar enthalpy of vapourisation of water at $$1$$ bar and $$373K=41\ kJ.{mol}^{-1}$$ and $$R=8.3J{mol}^{-1}$$ $${K}^{-1}$$)

A
$$4.100\ kJ$$ $${mol}^{-1}$$

B
$$3.7904\ kJ$$ $${mol}^{-1}$$

C
$$37.904\ kJ$$ $${mol}^{-1}$$

D
$$41.00\ kJ$$ $${mol}^{-1}$$

Solution

The change :
$$H_2O(l) → H_2O(g)$$

$$\Delta H = \Delta U + \Delta ngRT$$
"or" $$\Delta U = \Delta H - \Delta ngRT$$

Substituting the values, we get
$$\Delta U = 41.00\, kJ/mol -1\times 8.3\, J/mol/K \times 373\, K\times \frac{1}{1000}$$
$$= 41.00\, kJ mol^{-1} − 3.096\, kJ mol^{-1}$$
$$= 37.904\, kJ/mol$$
Question 7
1 / -0

$$\Delta {G}^{o}$$ of $${Cu}_{(aq)}^{+}$$ and $${Cu}_{(aq)}^{2+}$$ respectively are $$+50$$ and $$+66kJ/mole$$. Value of ($$\Delta{H}^{o}-T\Delta {S}^{o}$$) for $${Cu}_{(aq)}^{+}\rightarrow {Cu}_{(aq)}^{2+}$$ in kilo joules is?

A
$$-16$$

B
$$+116$$

C
$$-116$$

D
$$+16$$

Solution
Question 8
1 / -0

For a gaseous reaction,
$$A(g)+3B(g)\rightarrow 3C(g)+3D(g)$$

$$\Delta E$$ is $$17kcal$$ at $${27}^{o}C$$, assuming $$R=2cal$$ $${K}^{-1}$$ $${mol}^{-1}$$, the value of $$\Delta H$$ for the above reaction is:

A
$$15.8kcal$$

B
$$18.2kcal$$

C
$$20.0kcal$$

D
$$16.4kcal$$

Solution
Question 9
1 / -0

$$\Delta{S}_{surroundings}=+959.1J{K}^{-1}{mol}^{-1}$$
$$\Delta{S}_{system}=-163.1J{K}^{-1}{mol}^{-1}$$. Then process is?

A
Spontaneous

B
Non spontaneous

C
At equilibrium

D
Cannot be predicted from the information

Solution
Question 10
1 / -0

For the spontaneous process $$2F(g)\rightarrow {F}_{2}(g)$$, the sign of $$\Delta H$$ and $$\Delta S$$ respectively are?

A
+ve, -ve

B
+ve, +ve

C
-ve, -ve

D
-ve, +ve

Solution